1. Field of the Invention
The present invention generally relates to a head rest stay retaining mechanism, and more particularly to a head rest stay retainer which is provided atop the back of a seat, and which retains the head rest stay in such a manner that the stay can be moved vertically in relation to the seat back, when the head rest height is to be adjusted.
2. Description of the Prior Art
Such devices have been proposed; one of them is disclosed in the Japanese Utility Model Publication No. Sho-51-24664, for example, which consists, as illustrated in FIG. 1, of an engagement retainer 100 which is provided on the top face of a seat back 1 and retains a head rest 2 at the stay 3 thereof, and a support cylinder 101 provided within the seat back 1 to vertically guide the head rest stay 3. The engagement retainer 100 comprises a casing 111 which encloses the stay 3 of head rest 2, an engagement plate 112 housed in the casing 111 in such a manner that it may be displaceable perpendicularly to the axis of the stay 3, said plate 112 having a locking hole 114 through which the stay 3 penetrates or extends, and a spring 113 which forces the engagement plate 112 in the direction of engagement with one of cuts or recesses 31 provided in the stay 3. As obvious to those skilled in the art, this prior-art device is disadvantageous in operation and structure; namely, in order to vertically move the head rest 2, the peripheral edge 114a of the locking hole 114 must be disengaged from the cut 31 each time by forcing the engagement plate 112 against the action of the spring 113. Further, the structure of this device is rather complicated.
Besides, since the engagement of the peripheral edge 114a of the locking hole 114 in the engagement plate 112 into the cut 31 in the stay depends upon the magnitude of the force of the spring 113, the effort necessary to push the operating piece 115 attached to the engagement plate 112 in the direction of the casing 111, in order to disengage the peripheral edge 114a from the cut 31 and vertically move the stay 3, must be as great as the degree of engagement with the stay 3, which means a poor operability of the device. Namely, when operating the prior-art device in FIG. 1, a very great effort by the finger is required, and it is inconvenient that the stay 3 must be vertically moved while pressing the operating piece 115 to the casing 111, to move the engagement plate 112 directly against the force of the spring 113. For accurate engagement and disengagement between the cut 31 in the stay 3 and the peripheral edge 114a of the locking hole 114, the engagement plate 112 must be moved straight. To this end, a pair of springs 113 which have the same spring force is needed. Further, to assure that the engagement plate 112 will not be moved as deviated, but will move straight under the action of the springs 113, there must be provided in the engagement plate 112 a slot 116 of a length corresponding to the displacement of the plate 112, and a pin 117 which will engage in the slot 116 must be press-fitted from the top of the casing 111. Thus, the structure of the head rest stay retaining device is very complicated.